expected: |
  2,a
  ,b
  ,
query: |
  -- If no rows matched for group key should return NULL value. [0, 1]
  SELECT sum(id),str FROM read_text(E'id,str\n1,a\n1,a\n,b\n', fmt=>csv()) group by str
  union all
  -- If no grouping and no data - just return NULL. [2]
  SELECT sum(id),'' as str FROM read_text(E'id,str\n1,a\n', fmt=>csv()) where id > 100
  union all
  -- If grouping and no data - return nothing. []
  SELECT avg(id)::integer,'' as str FROM read_text(E'id,str\n1,a\n', fmt=>csv()) where id > 100 group by str;
